Process for the preparation of capryl salicylate



Patented 'July 31, 1945 SALICYLATE Stephen J. Wayo, Whiting, Ind., andFranklin M. Watkins, Chicago, Ill., assignors to Sinclair RefiningCompany, New York, N. Y., a corpora tion of Maine No Drawing.Application May 13, 1942, Serial No. 442,864

6 Claims. (01. 260-474) This invention relates to an improved method ofpreparing the secondary octyl ester of salicylic acid known as caprylsalicylate." It relates more particularly to an improved processinvolving the reacting of capryl alcohol (secondary octyl alcohol) withmethyl salicylate in the presence of a catalyst. The ultimate results ofthe reaction may be graphically represented as follows:

Capryl alcohol Methyl salicylate C-OClHi1 CHaOH Methyl alcohol Csprylsalicylate Reactions such as represented above are gen-' erallydesignated alcohol exchange or alcoholy and will be so designatedherein.

The present invention constitutes an improvement in the processdescribed and claimed in 00- pending application Serial'No. 421,372,flled December 2, 1941, i the name of Robert H. Gardner and Franklin M.Watkins, one ofthe Joint inventors of the present application, saidprocess similarly involving alcoholysis between a primary alcohol esterof salicylic acid and a secondary alcohol in the presence of a catalyst.

Alcoholysis, whereby one primary alcohol radical is substituted foranotheig-is a recognized procedure in organic chemistry; However, thelimitations of its use have been fully recognized. For example, thetendency of a secondary alcohol to replace a primary alcohol byalcoholysis has, prior to the'invention described in said pendingapplication, been found to be negligible or else so slight .as to be ofno practical commercial significance.

.- According to the process of said pending application, the secondaryalcohol is reacted with the primary alcohol ester of salicylic acid inthe presence of the catalyst under conditions of tem-' perature andpressure such that the primary alcohol formed by the reaction isdistilled off from the zone of reaction substantially as rapidly asiormed.

One of the catalysts found to be particularly useful in the process aspreviously employed is metallic sodium. As is well recognized, the .useof metallic sodium, particularly in a moist environment, constitutes afire and explosion hazard. It isan object of the present invention so tomodify and improve the process as to avoid the use of metallic sodium orother hazardous materials in environments apt to result in fire orexplosions.

We have discovered that, under carefully controlled conditions, thealcoholysis reaction between methyl salicylate and capryl alcohol,resulting in the production of capryl salicylate, may be eflected bytheme of sodium hydroxide as thecatalyst. Under conditions hereinafterfully described, we have found the use of sodium hydroxide catalyst toresult in the conversion of the,

methyl salicylate to capryl salicylate with yields closely approximatingthe theoretical yields, of high purity and with only minor losses ofmethyl salicylate and capryl alcohol.

, The use of sodium hydroxide is the catalyst for this alcoholysisreaction presents certain difliculties which, if special precautions arenot taken, result in economic, if not complete, impracticability of theprocess for the production of capryl salicylate. If an aqueous solutionof sodium hydroxide be added to a hot solution or methyl salicylate andcapryl alcohol, the methyl salicylate is saponifled by the sodiumhydroxide which is thereby quantitatively converted to sodiumsalicylate. Even when sodium hydroxide is added as a methyl alcoholsolution to a mixture of methyl salicylate and capryl alcohol at arelatively low temperature, at least partial saponiiication occurs. Thesodium salicylate formed is not an active catalyst. The saponiflcationdepletes the active NaOI-I catalyst and further uses up valuable methylsalicylate. In accordance with our improved process, saponification ofthe methyl salicylate is substantially prevented.

In accordance with our improved process, the sodium hydroxide catalystis with advantage added as an alcoholic solutionx Methyl and ethylalcohols have been found -suitable for this pin- It is generallyrecognized that sodium hydroxide reacts with such alcohols to a greateror less extent to form the corresponding alcoholate and water. Thisreaction may proceed in a methyl orethyl alcohol solution to an extentas great as Reference herein and in the appended claims to, alcoholicsodium hydroxide solutions will be un-. derstood to include su hreaction products as may be formed therein.

Also reference herein to water be present in the 4 action zone prior tothe product is separated methyl salicylate may be prevented ormateriallyretarded by maintaining conditions within the reaction zonesuch that any water present in the reacting materials is expelled priorto the introduction of the sodium hydroxide catalyst, any waterintroduced with the catalyst is instantly expelled, and any water formedduring the reaction is eliminated from the reaction zone substantiallyas rapidly as'formed.

In accordance with the present invention, this is eil'ected by heatingthe mixture of alcohol and ester to a temperature well above the boilingpoint of water, advantageously to 275 F. or higher, prior to theaddition of the sodium hydroxide catalyst and maintaining in thereacting zone a temperature of that order throughout the reaction. Therapid elimination of water may be further aided by carrier such as lowthe like, operating conditions and which assists in the vaporization andremoval of water by well known partial pressure eil'ects. The use ofvolatile inert carriers also aids in the rapid elimination of the methylalcohol.

desirable for the purposes stated. a

It is an essential of our improved process, as previously noted, that nosubstantial amount of reaction zone when the anhydrous condition may beaccomplished by the use of anhydrous reacting materials ,or bydehydrating the methyl salicylate and capryl alcohol mixture in thereaddition of the catalyst. In eflfectlng the dehydration of the mixturean inert carrier, such as previously mentioned, may

catalyst is added. This be used with advantage.

Though the introduction of the catalyst in alcoholic solution has beenfound vantageous, solid NaOH may if desired be charged to the reactionzone, preferably in a substantially However, the use of solid anhydrousNaOH does not eliminate the necessity of precaution with respect to thepresence of moisture, as there appears to be some formation of water byintermediate or side reactions. Whatever the source of water, it must beinstantly expelled if saponiflcation of the methyl salicylate is to beprevented. I

After the alcoholysis reaction has been completed, whichis indicated bythe cessation of the methyl alcohol distillation, the capryl salicylatefrom the catalyst and any alcohol or methyl salicylate. as

, anhydrous form.

unreacted capryl hereinafter more fully described.

. The invention has been found particularly valuable for the safe andeconomical preparation of capryl salicylate used in the preparation ofad particularly addends for lubricating oils for which application forLetters Patent Serial No. 409,856 was flled September 6, 1941,by-William L. Finley.

The process of-the present invention will be illustrated by thefollowing specific examples:

To a 5 liter-flask there was charged 1560 grams of CP3 capryl alcoholand 912 grams of U. S. P. methyl salicylate. The capryl alcoholcontained 16 grams of water equivalent to 1% by weight, 119

grams of capryl ketone equivalent to 7.7% by weight and 1425 grams ofcapryl alcohol equivalent to 91.3% by weight. The molar ratio of caprylalcohol and methyl salicylate added to the flask was 1.85:1.

The mixture in the flask was then heated to a temperature of 275 presenthad been expelled. 72 grams of methyl alcohol-sodium hydroxide solutionwas introduced through a separatory funnel, the time required for theaddition being 5 minutes.

The alcoholic-sodium hydroxide solution contained 12 grams or 16.6% byweight of sodium hydroxide and the molar ratio of the sodium hydioxidecatalyst thus added to the methyl salicylate was 0.05:1. This totalcharge was 2544 grams.

The heating of the flask was continued and methanol was distilled oil.In about 1 hour, a temperature of 350 was reached and this temperaturewas maintained for about 3 hours at which time methanol practicallyceased to be distilled oil. The amount .of crude methanol thus distilledfrom the flask was 306 grams and analysis showed it to consist by volumeof 17.5% capryl alcohol, 5.4% water and 77.1% methanol.

, After allowing for the methanol added as alcoholic-sodium hydroxidesolution, the crude methanol yield from the esterification reaction wasfound to be 57.5% by volume which indicates that 92.2% by weight of themethyl salicylate was converted to capryl salicylate. The weight ofcrude capryl salicylate remaining in the flask as bottoms was 2223grams. The reaction loss was equal to only 0.6% by weight.

A 2133 gram portion of the crude ester bot toms was washed once with 500c. c. of dilute (1:4) hydrochloric acid to convert any sodium phenatepresent to free ester and was then washed with- ,water until neutral.'I'he'loss by washing was 15 gramsor 0.7% by weight.

A 1742 gram portionof the washed ester was then charged .to a 5 literflask fitted with a steam delivery tube extending well below the surfaceof the liquid. The flask was then heated and, when the liquidtemperature had reached 230 F., steam was introduced through thedelivery tube. After a period of 45 minutes of this steam distillationand external heating, the temperature of the liquid within the flask was300 F. It was held at this temperature for 2 /2 hours until testsindicated that all unreacted capryl alcohol and methyl salicylate hadbeen distilled off. The overhead product totalled 857 grams or 49.2% byweight of the charge to the steam distillation and the amount of bottomsremaining in the flask was 879 grams or 50.4% by weigh-t, indicating a.total distillation loss of 6 grams or 0.4% by weight.

The distillation bottoms was substantially p capryl salicylate, havingan acid number of 0.8

and a; saponiflcation number of 223.1 as against a theoreticalsaponiflcation number of 224, indicating the composition to be 99.8% byweight of capryl sallcylate and 0.2% by weight of salicylic acid.

The overhead from this steam distillation. as

F. and, after any water previously indicated, contained unreacted caprylalcohol and methyl salicylate and also 228 grams of capryl salicylate,as well as 2.1% by weight of water and 10.2% by weight of ketone. Itsacid number was 2.3, its saponification number 55.5 and its phenolnumber 330. This overhead may with advantage be recharged to theoperation during a subsequent run, preferably after the removal of thewater and ketone and recovery of the capryl'salicylate therefrom, andthe unreacted capryl alcohol and methyl salicylate thus utilized.

The overall loss in the process was only 1.7% by weight and the finishedcapryl salicylate yield of 1097 grams, together with the 228 grams ofcapryl salicylate in the overhead from the steam distillation, made atotal yield of 1325 grams, equal to 52.1% by weight of the originalcharge, which is equivalent to a conversion of 88.3% by weight of methylsalicylate charged.

In a similar operation, wherein the molar ratio of capryl alcohol tomethyl salicylate was 2:1, the molar ratio of the sodium hydroxide addedin methanol solution to methyl salicylate was .05z1, the averagetemperature was 330 F., with a final or maximum temperature of 369 F.,and the reaction time was 6.5 hours, the yield of the methyl alcohol was83.6% by weight of the theoretical yield and the yield of caprylsalicylate was 84.6% by weight of the theoretical yield, the latterhaving an acid number of 0.8 and a saponification number of 220.3. Inthis run the sodium hydroxide was added as a 20% methanol solution overa 2 hour period.

A commercial sized operation, in accordance with our present invention,was carried out in a 1300 gallon horizontal gas-fired iron shell stillfitted with an unpacked brass tower 10 inches in diameter and 6 feet in'height. vTo this still there was charged 2210 pounds of methylsalicylate and 3760 pounds of capryl alcohol of the quality previouslynoted, the molar ratio of alcohol to ester being 1.82:1. After thismixture had reached a temperature of 317 F., and any moisturepresentexpelled, 179 pounds of a solution of 29 pounds of sodiumhydroxide in 150 pounds of methanol was added over a period of 30minutes, the molar ratio of sodium hydroxide to ester being 0.05: 1.Heating was continued and in about 4 hours a temperature of 375 F. wasattained. The mixture was held at this temperature for an additional 3hours until no further methanol distilled off.

The overhead product amounted to 210 gallons and consisted primarily ofmethanol, capryl alcohol and a small amount of water. The meth- 5 anoland capryl alcohol were recovered by fractionation. The bottomsremaining in the still contained sodium capryl salicylate, caprylketone, unreacted capryl alcohol, unreacted methyl salicylate and caprylsalicylate and amounted to 590 gallons. From another run, under similarconditions, 220 gallons of overhead and 565 gallons of bottoms wereobtained- A 1055 gallon portion of the bottoms from these two runs wascharged to a 1500 gallon glasslined Pfaudler kettle fitted with astirrer to provide agitation and the bottoms washed, first with 210gallons of dilute sulfuric acid (10 gallons of 93% sulfuric acid in 200gallons of water) and then with two successive 500 gallon portions ofwater. The yield of ester from this washing operation was 1045 gallons.

A 1000 gallon portion of the washed ester was then charged to the 1300gallon horizontal still previously described and heated to 300 F. Steamwas then introduced and the external heating continued until a liquidtemperature of 370 F. was attained. The liquid was held at thistemperature until all of the unreacted capryl alcoholand methylsalicylate had been distilled off. The total time required for thisdistillation was 7 /2 hours.

From this steam distillation there was obtained an overhead of'250gallons of water and 2490 pounds of recycled alcohol. The lattercontained capryl ketones, unreacted capryl alcohol and methyl salicylateand a small proportion of capryl salicylate and was used as part of thecharge for succeeding runs.

The yield of capryl salicylate remaining in the still after the steamdistillation was 4681 pounds, equivalent to a conversion of 73.7% byweight of the methyl salicylate charged to capryl salicylate. Thiscapryl salicylate product has an acid number of 2.2 and a saponificationnumber of 219.5, indicating a purity of 98% by weight and the presenceof 0.5% by weight of salicylic acid.

The sodium hydroxide used in the foregoing specific examples was thecommercial grade caustic soda of 76% Nazo and the amounts used were onan anhydrous basis.

The optimum proportion of catalyst used depends somewhat upon operatingconditions. Generally, ratios of from 0.025 to 0.2 mole of sodiumhydroxide per mole of methyl salicylate have been found effective. a

It is generally desirable to'use a substantial excess of the caprylalcohol. In the foregoing specific examples approximately 1.85 mole permole of methyl salicylate has been used. Good yields may be obtainedusing smaller excesses of the capryl alcohol, for example aslow as 0.1mole.

However, it is usually preferable to use about 1.5 to 2 moles of caprylalcohol per mole of methyl salicylate. Since excess capryl alcohol maybe substantially completely recovered for reuse, a substantial excess isgenerally recommended.

The temperature at which the process is carried out may likewise bevaried somewhat. Generally, the rate of reaction and the yield arefavorably affected where temperatures within the range of 275 F.. to 375F. are employed. It is essential that the temperature be substantiallyin excess of the boiling point of water, as previously stated, so asrapidly to expel from the zone of reaction any water formed. However,care must be exercised to avoid temperatures sufficiently high to causedehydration of the capryl alcohol resulting in the conversion of thealcohol to olefins and the formation of water. Temperatures within therange of about 250 to 400 may be used with advantage and, if operatingat reduced pressures, even lower temperatures may be employed.

In the foregoing specific examples, the pressure employed wassubstantially atmospheric. Subatmospheric press ires may be employedwithout departing from the spirit of this invention and may be foundadvantageous for the rapid removal of water and methyl alcohol where itis desired to lower the operating temperature.

In the foregoing description of our improved process. the sodiumhydroxide has been designated a catalyst. While it cannot be stated withcertainty that the sodium hydroxide functions as a true catalyst, it hasbeen proven that, by its use in minor proportions, as herein described,the desired reaction is-promoted and a highly effective process for theproduction of capryl salicylate results.

We claim:

1. Inthe process of preparing capryl salicylate by heating asubstantially anhydrous mixture of capryl alcohol and methyl calicylatein the presence of a, catalyst whereby the methyl radical of the esteris replaced by the octyl radical of the capryl alcohol and methylalcohol is liberated and expelled from the zone of reactionsubstantially as rapidly as formed, the improvement comprising heating amixture of methyl salicylate and capryl alcohol to a temperature wellabove the boiling point of water,, adding thereto a minor proportion ofsodium hydroxide and maintaining the temperature of the mixture duringthe reaction well above the boiling point of water but below that atwhich substantial dehydration of the alcohol would occur.

2. In the process of preparing capryl salicylate by heating asubstantially anhydrous mixture of capryl alcohol and methyl salicylatein the presence of a catalyst whereby the methyl radical of the ester isreplaced by the octyl radical of the capryl alcohol and methyl alcoholis liberated and expelled from the zone of reaction substantially asrapidly as formed, the improvement comprising heating a mixture of themethyl salicylate and capryl alcohol to a temperature well above, theboiling point of water, adding thereto sodium hyin alcoholic solutionand maintaining the temperature of the mixture during the reaction wellabove the boiling point of water but below that at which substantialdehydration of the alcohol would occur.

3. In the process of preparing capryl salicylate 'by heating asubstantially anhydrous mixture of capryl alcohol and methyl salicylatin the presence of a catalyst whereby the methyl radical of the ester isreplaced by the octyl radical of the capryl alcohol and methyl alcoholis liberated and expelled from the zone of reaction substantially asrapidly as formed, the improvement comprismethyl salicylate and caprylalcohol to a temperature within the range R, adding thereto a minorproportion of sodium hydroxide and maintaining the temperature of themixture within the abovestated range during the reaction.

4. In the process of preparing capryl salicylate by heating asubstantially anhydrous mixture of capryl alcohol and methyl salicylatein the presence of a catalyst whereby the methyl radical of assume theester is replaced by the octyl radical of the capryl alcohol and methylalcohol is liberated and expelled from the zone of reactionsubstantially as rapidly as formed, the improvement comprising heating amixture of methyl salicylate and capryl alcohol in which the molar ratioof the alcohol to the ester is in excess of unity'to a temperaturewithin the range of about 250 to 400 'F., adding thereto aminor-proportion of sodium hydroxide. and maintaining the temperature ofthe mixture within the above-stated range during the reaction.

5. In the process of preparing capryl salicylate by heating asubstantially anhydrous mixture of capryl alcohol and methyl salicylatein the presence of a catalyst whereby the methyl radical of the ester isreplaced by the octyl radical of the capryl alcohol and methyl alcoholis liberated and expelled as rapidly as formed, the improvementcomprising heating a mixture of capryl alcohol and methyl salicylate inwhich the ratio of the alcohol to the ester is in excess of unity to atemperature within the range of about 275 to 375 F., adding theretosodium hydroxide in proportions such that the molar ratio of sodiumhydroxide to methyl salicylate is within the range of about 0.025-0.2:1and maintaining the temperature of the mixture within the above-statedrange during the reaction.

6. In the process of preparing capryl salicylate by heating asubstantially anhydrous mixture of capryl alcohol and methyl salicylatein the presence of a catalyst whereby the methyl radical of the ester isreplaced by the octyl radical of the capryl alcohol and methyl alcoholis liberated and expelled from the zone of reaction substantially asrapidly as formed, the improvement comprising heating a mixture ofcapryl alcohol and methyl salicylate in which the molar ratio of thealcohol to the ester is about 1.85:1 to a temperature within the rangeof about 275 to 375 F., adding thereto sodium hydroxide in alcoholicsolution in proportions such that the molar ratio of sodium hydroxide tomethyl salicylate is about 0.05:1 and maintaining the temperature of themixture within the above-stated range during the reaction.

STEPHEN J. WAYO. FRANKLIN M. WATKINS.

from the zone of reaction substantially

